Talk:Radical symbol

Article name

Should be under radical sign? —DIV (115.64.145.215 (talk) 07:55, 9 December 2017 (UTC))

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Principal square root?

We currently have "The square root symbol refers to the principal square root, which is the positive one." with no supporting reference. My recollection from school is that the square root symbol refers to both square roots of a positive number: thus √64 = +/- 8. I can see why there might be a convention: but I am unaware when, why and by whom this convention (positive root only) might have arisen if, in fact, it did. Cross Reference (talk) 03:34, 24 May 2024 (UTC)

@Cross Reference: I was surprised to learn today that the radical mark is indeed intended by convention - to prove this to yourself recall the quadratic formula and catch yourself saying "plus or minus" - to be only the principal root. With that said I agree we would benefit from a citation, the history is incredibly hard to track down, even harder than the origin of the left-to-right convention for operators of similar precedence (the convention that makes 1 - 2 - 3 equal to -4). A [citation needed] being resolved by some future Wikipedian would be invaluable. And all _that_ said, this is _incredibly sloppy_ and must be reworded, I do not even know where to begin, "The two square roots of a negative number are both imaginary numbers, and the square root symbol refers to the principal square root, the one with a positive imaginary part" Sqrt(4) being both 2 and -2 has nothing, at all, to do with imaginary numbers, and the quoted sentence does not tell us that 2 is what is meant by the principal square root. I will not go so far as to call the current wording vandalism but that leaves me unable to say what it is other than wrong. 2601:283:100:73F0:8F70:B35E:BF56:7F3F (talk) 20:32, 28 July 2024 (UTC)

In the context of the rest of the piece and accepting for the time being that the radical sign refers only to the positive square root - and, for the record, I do not accept that - then I don't have a problem with ""The two square roots of a negative number are both imaginary numbers, and the square root symbol refers to the principal square root, the one with a positive imaginary part". Thus √(-64) = +8i and not -8i which is, at least, consistent with the rest of this convention if, indeed, it is an accepted convention. But I still want to see a citation. I tend to answer silly Facebook 'today's mathematical problem' posts and have frequently been reprimanded in the comments for such absurdities (/s if you need it) as √121 = +/- 11. Cross Reference (talk) 10:26, 13 October 2024 (UTC)